The field of this invention is related to a hydrometallurgical process of extracting and leaching, and a process of liquid-solid separation with flocculation.
A widely used process for the extraction of uranium from uranium-bearing ores involves crushing and grinding the ore very finely, making a slurry or "mill feed pulp" from the finely ground ore and then leaching the pulp under agitation in order to dissolve the uranium which is present in the ore. The pulp is then treated with flocculants to aid in the separation of the pregnant solution of uranium from the ore tailings. The uranium is then separated from the pregnant solution by, for example, precipitation or ion exchange.
Dissolution of the ground ore can be carried out in either acid or alkaline leaching circuits. In ores cemented with clay, silica, or organic material, the acid leach may be preferred. Limestone containing ores or sandstone ores with a high percentage of calcite as grain-cementing material are generally leached in alkaline circuits.
Sulfuric acid is universally used in the acid leaching process. Sodium carbonate and sodium bicarbonate are used in the alkaline or "carbonate" leaching process. A liquid-solids separation problem generally arises in the thickening or filtration of leached uranium ore slurry. Since the loss of weight in leaching is usually small, virtually all of the ore must be handled by a multistage process to recover a pregnant solution of suitable uranium content while making a throw-away tailings product. Preroasting the ores and using common flocculating agents such as starches and glues have helped to accelerate the thickening and filtering of some ores, but have shown little benefit for others. Certain polysaccharides, such as locust bean gum, guar gum and cactus extract, as well as synthetic polymers, such as polyacrylamide, have been found to be better thickeners and flocculants than glues and starches.
Information pertaining to uranium ore processing can be found in "Uranium Ore Processing", edited by J. W. Clegg and D. D. Foley, Addison-Wesley Publishing Company, Inc., Reading, Massachusetts (1958) and in "The Extractive Metallurgy of Uranium" by R. C. Merritt, Colorado School of Mines Research Institute (1971).